Nuclear Plague

After a third World War breaks out in the year 2093 primarily between New America and Russia things look bad as nuclear warfare starts to drift closer and closer to the main option to win. One of the ways the Americans plan to defend against such a thing is to find the secret to immortality, however in a major turn of events Russia launches the nukes right as the secret was found in a lab. In retaliation, New America launches their nukes as well which effectively sends the world into a post apocalyptic nightmare.
The year is now 2189 and now all of the people during that era are dead. All but one, a scientist in the lab where the immortality research was happening managed to wake up nearly a century after the bombs fell and found out that he became immortal when the building he was in exploded. Now he is humanity's last hope for long time survival.